A computer model that convinced engineers that the Columbia shuttle could safely return to earth lacked the right information, accident investigators say. The analysis carried out during the flight concluded that little harm had been done when a piece of foam came off the fuel tank during lift-off.

But the model had not been used before to assess damage from falling debris during a flight, said former astronaut Sally Ride, a member of the board investigating the accident. Columbia broke up during re-entry on 1 February, killing all seven astronauts on board. In recent weeks investigators have been focusing on damage done by the falling foam to the left wing of the shuttle.

A group of Boeing engineers carrying out a computer analysis during the flight realised they needed more data about where the foam had hit, Ms Ride told reporters in Houston, Texas. She said they asked the US space agency Nasa to take pictures of the orbiting shuttle to assess the potential damage - but no pictures were ever taken, she said. She said this was the result of "miscommunication" between the engineers and Nasa.